1. Field of the Invention
This invention relates to an ink supply device for supplying ink to a recording head in an ink jet recording apparatus.
2. Description of the Related Art
In a conventional ink supply mechanism used with an ink jet recording apparatus, an ink absorber is loaded into an entire ink tank communicated with a recording head and is previously impregnated with ink and the ink in the ink absorber is supplied to the recording head, for example, as described in Japanese Patent Laid-Open No. Sho 63-87242. Porous material such as a sponge, fibrous material such as felt, or the like is used as the ink absorber. With such an ink supply mechanism, ink only in an amount as much as about 40%-60% of the capacity of the ink tank can be used so that use efficiency is low. Thus, if an attempt is made to prolong the life of the ink tank, inevitably the ink tank becomes large-sized, as a result of which a demand for miniaturization is not met.
Since the conventional ink supply mechanism holds ink by capillary attraction of the ink absorber, appropriate negative pressure is generated for the recording head. Thus, when the amount of ink held in the ink absorber decreases with consumption of the ink, negative pressure acting on the ink with which the ink absorber is impregnated rises gradually from a decrease in water head, impeding ink supply to the recording head. When the phenomenon develops and the negative pressure applied to the ink exceeds a given value, bubbles flow reversely from a print nozzle section of the recording head and the spout operation of ink is performed with no ink supplied to the recording head. Thus, spout failure causes a record image to become defective, lowering the picture quality. This phenomenon also causes the use efficiency of ink to lower.
To solve such problems, in ink supply devices described in Japanese Patent Laid Open Nos.Sho 59-500609, Hei 1-148559, 3-180357, etc., for example, a hermetically sealed ink tank is filled only with ink and a capillary having one end open to the air is communicated with the ink tank or the ink tank is formed with a small hole. According to the ink supply devices, when negative pressure in the ink tank increases with consumption of ink in the ink tank, air is introduced through the capillary or small hole into the ink tank for holding the negative pressure value in the ink tank substantially constant, enabling the ink in the ink tank to be stably supplied to the recording head.
When environment changes, for example, if air in the upper space of the ink tank expands, the ink in the ink tank flows reversely through the capillary. Thus, there is a chance that the reversely flowing ink will spout in the ink supply device described in Japanese Patent Laid-Open No. Sho 59-500609 or in one example of the ink supply device described in Japanese Patent Laid-Open No. Hei 1-148559 because the air and the ink tank are communicated with each other only via the capillary. Although the capillary may be lengthened, the structure becomes complicated.
Another example of the ink supply device described in Japanese Patent Laid-Open No. Hei 1-148559 or the ink supply device described in Japanese Patent Laid-Open No. Hei 3-180357 has a small chamber. If air in the upper space of the ink tank expands, the ink in the ink tank is temporarily saved in the small chamber, thereby lowering pressure in the ink tank, thus effectively preventing ink from leaking from the recording head or the capillary or small chamber communicated with the air.
However, the ink supply devices have the small chamber disposed in the lower portion of a main ink chamber. Therefore, when the ink moved to the small chamber to relieve pressure change in the ink tank is restored to the main ink chamber, the ink must overcome capillary attraction and be moved against the gravity direction. Thus, the ink in the ink tank cannot completely be restored to the main ink chamber and some of the ink remains in the small chamber. That is, the capacity efficiency is lowered by the remaining amount of ink.